Known methods for active 3D measurement systems that uses laser light or halogen light sources are (1) light radar methods, (2) active stereo methods, (3) photometric stereo methods, (4) more topography methods, and (5) interference methods. Particularly, active stereo methods have been widely studied and commercialized because of their usefulness and accuracies.
Systems based on active stereo methods are composed of light sources (for example, lasers or halogen lamps) and image capturing devices (for example, cameras or CCDs). Since 3D shape acquisitions using active stereo methods are based on triangulations, the relative positions between the light sources and the image capturing devices should be known in advance (extrinsic calibrations). To realize this condition, the systems of active stereo methods often becomes large, heavy, and complicated.
If the relative locations between the light sources and the image capturing devices can be obtained easily, 3D shape acquisition systems can be simplified. Based on this idea, several methods have been proposed, for example, Japanese patent disclosure No. 2003-130621, in which the relative location of the light source from the image capturing device is obtained by capturing the markers attached on the light source at the same time.
If we can obtain the relative position between the image capturing device and the light source without either capturing markers or performing an extrinsic calibration, the system becomes more useful, and many of the disadvantages of the conventional active measurement systems can be overcome in terms of simplicity, portability, and inexpensiveness.
Patent documents 1: Japanese patent disclosure No. 2003-130621